The invention relates to an infinitely variable toroidal drive.
Such an infinitely variable toroidal drive usually has input and output discs coaxially disposed relative to a common shaft which are arranged in pairs and have toroidally shaped inner surfaces, the same as friction wheels placed between the pairs of input and output discs. The friction wheels are in frictional contact both with the input and output discs and transmit to the output disc the torque transmitted to them by the input disc, the rotational speed of the friction wheels being higher the larger the distance between their contact point with the input disc and the axis of rotation. Accordingly, by swiveling the friction wheels, it is infinitely and arbitrarily possible to adjust the rotational speed of the output disc. To this end, the axes of rotation of the friction wheels are supported in a carrier which can be controlled via a swiveling device.
The basic principle of such an infinitely variable toroidal drive has already been described in U.S. Pat. No. 2,152,796 which was published in the year 1939. In this publication are provided two pairs of concave input and output discs between which are placed pivotably supported friction wheels so that a torque transmitted via one input shaft to the input discs and the friction wheels, according to the relative position of the friction wheels with a reduction ratio depending thereon, is fed via the output discs, a gear wheel step and a hollow shaft to a summarizing transmission in the form of a planetary transmission. The web of the planetary transmission drives an output shaft which is connected with the driving wheels, e.g. of a motor vehicle. The output shaft can be situated parallel with and spaced from the input shaft. The output gear wheel and the two output discs are rotatably mounted on a sleeve supported on its ends in bearing brackets. The arrangement of the bearing brackets between each input and output disc requires a sufficiently large installation space between the discs.
The transmission according to U.S. Pat. No. 3,739,658 likewise has a pull-and-push variator with two input and output discs disposed in pairs between which are situated pivotably supported friction wheels. In this construction, a bearing bracket is present which is a component part of the housing and is horizontally disposed spatially between the two output discs. The power flowing from the output discs is fed to a hollow shaft, via a planetary transmission, which, in addition, acts as a differential. The hollow shaft is non-rotatably connected with the output gear wheel and is rotatably held in the bearing bracket by ball bearings.
The output gear wheel is in driving connection with one gear wheel which is non-rotatably fastened on the housing of a torque converter. The latter drives the output shaft of the transmission. The arrangement of the torque converter at the entrance of the output shaft requires a relatively large axial distance between input and output shafts of the transmission. Utilization is thereby sharply limited, since the installation space needed is not always available.
U.S. Pat. No. 4,893,517 has disclosed an infinitely variable toroidal drive having one input shaft which transverses a housing. The housing is divided by means of a partition wall into two cavities in each of which is situated one input disc and one output disc opposite thereto with friction wheels therebetween wherein both of the input discs and the output discs in the two cavities lie on a common axis toward which the friction wheels can be swivelled to obtain the desired speed ratio. Both pairs of input discs and output discs are situated in the cavities in mirror symmetry to each other in a manner such that the two output discs lie adjacent each other on opposite sides of the partition wall separating the two cavities from each other and in which a gear wheel is supported which is actuated by the two output discs jointly with the output torque.
The Applicant""s patent application No. DE 197 32084.8 describes an infinitely variable toroidal drive in which the input shaft is surrounded by a torque shaft disposed coaxially thereto; the input shaft extends through the entire infinitely variable drive and is provided at its end with an axial disc. With the axial disc is associated a contact-pressure device which pressurizes a first input disc of a transmission unit in direction to the appertaining output disc thereof. The input disc of the second transmission unit supports itself via an axial bearing on a second axial disc and via a radial bearing on the input shaft.
Between both transmission units is provided a cup-shaped bearing bracket member in which is situated one gear wheel actuated by the two output discs of both transmission units and which meshes with an output gear wheel of an output shaft. The bracket bearing member forms, together with an upper and a lower frame strap, a holding frame wherein the frame strap carries upper and lower transverse yokes where are situated the carriers for the friction wheels which can pivot on pre-selected planes in order to transmit the torque from the respective appertaining input disc with an infinitely variable ratio to the appertaining output disc of the transmission unit.
The problem on which this invention is based is to reduce the construction cost of such an infinitely variable transmission and lower the cost of production.
The invention solves the stated problem in a generic infinitely variable toroidal drive incorporating the present invention.
The advantage that can be obtained with the invention is that the use of a universal bearing on which an input disc absorbs both radial and axial forces makes it possible to shorten the total length of the infinitely variable transmission by eliminating the hitherto usual raised axial support. The elimination of the formerly usual radial bearing of the input disc further makes it possible to displace the locking system (ball-spline) obtained with the aid of balls with the torque shaft to a less loaded place of the input disc whereby the service life of the transmission is increased.